IMPACT ASSESSMENT OF COASTAL DIKE FAILURE BY A HIGH-RESOLUTION TSUNAMI FLOOD MODEL

Abstract

 Severe devastation by the 2011 Tohoku Tsunami highlited the importance of a robust and redundant coastal dike against a low-frequency extreme tsunami. To discuss its effectiveness, we need to clarify how coastal dike failure affects damages in its hinterland at the occurrence of significant overflows. The paper presents results of case studies of the 2011 tsunami event in which the impact of dike failure is analysed using a high-resolution flood simulation at two sites with different topographic features. The dike failure significantly increases flood intensity and thereby human and bulding damages on a vast coastal plain of the southern Sendai coast, while its impact is relatively small in narrow low-lying areas of Otsuchi located on ria coast. The model results describe flood impacts better when the dike failure is accounted for in the southern Sendai coast. We also analyse local scouring behind coastal dikes which may trigger the dike failure and show that it can be related with local flow velocity from the high-resolution flood model.